A significant disadvantage of the known ICS systems is the fact that the distance between the objective and the tube lens unit is only variable within narrow limits, and therefore these systems are tied to predetermined tube lens units and thus can only be used in instruments for which they were designed.
In WO2005/088378, a tube lens unit is described which achieves a chromatically compensating effect when used with objectives that focus an image at infinity and that have residual chromatic errors. However, the space between the microscope objective and the tube lenses where light rays are parallel is not corrected because the chromatic errors of the objective are compensated. It has proven disadvantageous that the space between the microscope objective and the tube lens is not variable. In addition, a lateral offset between objective and the tube lens unit generates a lateral chromatic aberration on the optical axis.
A corrected tube lens unit is further described in US 2010172029. In order to eliminate the chromatic aberration as much as possible, cost-intensive lenses with abnormal dispersion must be used. This solution is disadvantageous because, depending on the space between the objective and the tube lens, the variation of the astigmatism is not sufficiently reduced. Furthermore, there is less than desirable compensation of the lateral chromatic aberrations from the objective and the tube lens unit.